Estimating faecal sludge quantity on a city wide scale with the help of a volaser? Questions around sample size?

  • burton
  • burton's Avatar
    Topic Author
  • Posts: 9
  • Likes received: 1

Estimating faecal sludge quantity on a city wide scale with the help of a volaser

Estimating faecal sludge quantity can be hectic. Onsite sanitation containments have varying shapes and sizes around the world because they are constructed by different people according to what they want, and because they are under ground, it makes it difficult (if not impossible) to estimate the total amount of accumulated faecal sludge on a neighborhood or city-wide scale. A volaser is an instrument that was developed to measure volumes of faecal sludge inside latrines for the ultimate goal of aiding planning for improved sanitation services worldwide. It consists of a measuring head with a distance-laser module, a tripod-stand, and a telescopic rod to measure depth. To know more about the volaser visit

My question is on estimating the total quantity of faecal sludge from all containment facilities e.g pit latrines, after measuring the volumes with a volaser. With an existing number of over 1000 latrines,what could be the best and most accurate method of estimating the FQ given a sample size of 150 latrines. I thought averaging the obtained 150 latrine sludge volumes and multiplying by the total number of containments would misrepresent the actual total quantity because volumes of sludge differ significantly due to age of latrine, number of users and other factors. what do you think can be the best way to approach this?
The following user(s) like this post: sahidul93
You need to login to reply
  • muench
  • muench's Avatar
  • Moderator of this Forum; Freelance consultant and Wikipedian (former roles: program manager, lecturer, process engineer for wastewater treatment plants)
  • Posts: 2857
  • Karma: 53
  • Likes received: 760

Re: Estimating faecal sludge quantity on a city wide scale with the help of a volaser

Dear Burton and all,
Do you have access to such a volaser? Are they routinely being used yet?

Photo from the website that you linked to:

With regards to your question, I guess this is about sample size: what sample size do you need for a certain statistical significance of your results. Maybe dive into some statistics textbooks or websites to answer that (I did that at university but it's far too long ago! ;-) )

Another aspect is that you could compare your results with other methods, like the one proposed by EAWAG:
Methods to reliably estimate faecal sludge quantities and qualities for the design of treatment technologies and management solutions
(from their highlights: • Correlations to spatially available data can help predict quantities and qualities. • Indicators include income level, users, volume, emptying frequency, and truck size. • Correlations in characteristics could provide a way to reduce analytical costs.)

Hope this is useful.


Head moderator of this discussion forum
(Funded via consultancy contract with Skat Foundation funded by WSSCC)

Dr. Elisabeth von Muench
Independent consultant located in Brisbane, Australia
This email address is being protected from spambots. You need JavaScript enabled to view it. Twitter: @EvMuench
Sanitation Wikipedia project leader:
My Wikipedia user profile:
You need to login to reply
  • sahidul93
  • sahidul93's Avatar
  • Better Environment, Better Life
  • Posts: 20
  • Likes received: 3

Re: Estimating faecal sludge quantity on a city wide scale with the help of a volaser

Can I get answer about the result of Volaser. Is the Volaser commercially produced and available in the market? I see the proposal of SanDec on testing and app. I don't have any information. So, I want to know about this.


Md.Sahidul Islam P.Eng
B.Sc(Civil), M.Sc(Civil), MBA(HRM)
Assistant WASH Officer
UNHCR, Cox’s Bazar, Bangladesh
Mobile: +8801712124330 | Skype: sahidul93

Md.Sahidul Islam
Assistant WASH Officer
UNHCR, Cox’s Bazar, Bangladesh
Mobile: +8801712124330
You need to login to reply
Share this thread:
Recently active users. Who else has been active?
Time to create page: 1.637 seconds